1. Field of the Invention
This invention relates generally to liquid fillable mattresses and more specifically to watermattresses having a peripheral airframe.
2. Description of the Prior Art
In the past, watermattresses have included those providing a flexible bladder having a generally rectangular shape and being fillable with a liquid such as water. Such mattresses have demonstrated a tendency to roll off of a flat planar surface so that they typically have been used with a wood frame having upstanding side members. These side members, in combination with the base of the frame, have defined a cavity for receiving the water bladder. The upstanding side members make it difficult to get in and out of bed and are particularly uncomfortable when one attempts to sit on the edge of the bed.
Watermattresses of this type have been provided with unitary sheet configurations and a preferred lap seam construction as disclosed by B. Kuss in U.S. Pat. No. 3,753,823. A highly desirable bladder configuration providing a relatively square corner construction is disclosed by Craig S. Miller in copending application Ser. No. 754,015 filed Dec. 23, 1976 now U.S. Pat. No. 4,115,886.
In another type of watermattress construction, more analogous to the present invention, an airframe is provided peripherally of the water bladder. This construction has alleviated the necessity of providing the relatively hard and narrow upstanding side members of a wood frame. Thus, this mattress is suitable for use on a simple planar surface. Mattresses exemplary of this type of construction are disclosed by Cantillo in U.S. Pat. No. 3,918,110, and by Pennington in U.S. Pat. No. 3,925,835. Although these particular mattresses have provided the advantages associated with an airframe, their complicated constructions have resulted in relatively weak water bladders. As a result of the high pressures occurring in the area of the bladder, the materials forming these mattresses have tended to stretch and bow so that it has been difficult to maintain a rectangular configuration. As a consequence, even these airframe mattresses have been suggested for use with rigid frames having the upstanding side members. Such a combination is suggested for example, by Fraige in U.S. Pat. No. 3,864,768.
In some of these airframe constructions, an inner wall is provided which separates the water cavity from the peripheral air cavity. If the integrity of this inner wall is broken due to puncture or decay, the water in the bladder is free to escape into the air cavity at the peripheral regions of the mattresses. Once this has occurred, the advantages of an airframe are negated and the mattress is free to roll off of a simple planar surface.
In other types of mattress constructions, an air beam structure has been provided beneath the water bladder in an attempt to reduce the amount of water needed to fill the mattress. Such a construction is disclosed by Shields in U.S. Pat. No. 3,766,579. Mattresses of this type are complexed and difficult to manufacture. They also require a significant amount of material in their construction.